without knowing more than i've gathered from your previous posts i can obviously only give very limited advice, but a few thoughts:Having never dealt with (to my knowledge) a transgender person, it's hard for me to tell if I'm going to offend him or not when I try to ask questions.
- just because he doesn't seem to (want to) talk about it doesn't mean you're doing anything wrong. i imagine in a situation like that talking is always very difficult and it needs time and careful nuturing of your relationship to do so freely, if it's possible at all. time spent together without talking isn't necessarily wasted.
- if you've had frequent talks about everyday's life and stuff before, try to not let those die completely, unless he seems annoyed by keeping that up now. life goes on and there's so much more that matters about a person than gender :]
when something seems to affect your entire life so strongly and negatively, everything that gives your head and heart a small break now and then from all the shit can be worth a lot.
- i don't think it's possible to never say anything potentially stupid/wrong/offensive unless you avoid the topic altogether. important is that he knows you are there for him, and that you are trying your best. even if he doesn't seem to be willing to talk much, you can just tell him that.
- lastly, there are quite a few very nice people on mmoc that have experience with transgender issues themselves. maybe just talking with one of them about their own experience (without need of deeply psychological professional advice^^) can help you better understand what you, and more importanlty your son, are dealing with.
in any case, best of luck to the two of you, i hope it'll all work out well eventually =)